Miniature sensors such as gyroscopes useful for measuring or detecting movement or acceleration in particular have been fabricated by micromachining motion sensitive elements in integrated circuit chips. Such devices, based on vibrating mechanical elements which sense rotation, can be produced inexpensively by batch processing and yet yield performance suitable for many applications which require a low cost. One such application, for example, is the detection of yaw for sophisticated controls in automotive vehicles.
One sensor of this type incorporates a micromachined ring which is excited into vibration at its resonant frequency. The direction or orientation of vibration is somewhat dependent on rotation of the sensor so that the vibration can be analyzed to sense directional changes. An array of electrodes capacitively coupled to the ring are used to apply excitation energy and to sense the resulting vibration. A number of circuits are employed to excite the ring to resonance and to produce an output indicative of yaw or yaw rate.
Other types of motion sensors include other forms of vibrating elements such as tuning fork or vibrating shell configurations. The vibrating elements are not limited to microstructure devices but may be implemented as large scale devices as well. In any event, a failure in the vibrating element or in the excitation circuitry can lead to a loss of proper vibration. It is desirable to detect the occurrence of such a failure.